The Committee on Medical Aspects of Food Policy report Nutritional Aspects of Cardiovascular Disease recommended increased dietary intakes of the long chain polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid to help protect against cardiovascular disease. There is some evidence that a-linolenic acid can be elongated and desaturated by mammalian enzyme systems to produce small amounts of eicosapentaenoic and docosahexaenoic acids. Whole linseeds are rich in a–linolenic acid, and it has been suggested that feeding this oilseed to dairy cows may result in higher levels of the long chain polyunsaturated fatty acids in bovine milk. To examine this hypothesis, the effect of feeding whole ground linseed and xylose treated whole ground linseed on the performance and milk composition of dairy cows was investigated.

Either form of whole linseed reduced dry matter intakes and milk protein concentration. The xylose treated whole linseed increased milk yield, but neither linseed source changed milk fat concentration. Levels of milk a-linolenic acid increased to 1.2 g/100 g fatty acid when whole ground linseed was fed, and to 1.5 g/100 g fatty acid with the xylose treated linseed compared with 0.7 g/100 g fatty acid for cows fed the control diet. The efficiency of incorporation of additional dietary a-linolenic acid into milk fat was estimated to be 1.6 and 3.4% for the whole ground and xylose treated whole ground linseed respectively. Feeding whole ground linseed increased the proportion of a-linolenic acid in milk fat, but there was no evidence of eicosapentaenoic and docosahexaenoic acids in milk fat, suggesting that if any elongation and desaturation of a-linolenic acid occurs in dairy cows, none is transferred to milk.